Refrigeration system

ABSTRACT

A refrigeration system comprising: a Stirling machine ( 1 ); a refrigerating chamber ( 4 ); a first thermal energy transfer device ( 2 ) operatively associated with a refrigerating portion ( 1   b ) of the machine and with the refrigerating chamber ( 4 ); a second thermal energy transfer device ( 3 ) operatively associated with a heat receiving means, external to said machine, and with the heating portion ( 1   a ) thereof, the first thermal energy transfer device ( 2 ) comprising: at least one capillary pump ( 10 ) mounted in the refrigerating chamber ( 4 ) to evaporate, by the heat absorbed from the latter, the circulating fluid received in said capillary pump ( 10 ); a condenser ( 20 ) operatively coupled to the refrigerating portion ( 1   b ) of the Stirling machine ( 1 ) to condense the circulating fluid received, in the gaseous state, from the capillary pump ( 10 ); and pipes ( 30, 40 ) to conduct in a closed loop, the circulating fluid between the capillary pump ( 10 ) and the condenser ( 20 ).

FIELD OF THE INVENTION

The present invention refers to a refrigeration system that uses aStirling machine as a source of thermal energy to be transferred toenvironments located outside and spaced in relation to the compressor,particularly to the heat exchangers (heads) thereof.

BACKGROUND OF THE INVENTION

Stirling machines have been known for many years, operating in severalapplications. They are widely used as systems to produce movement(motors) and in the field of energy generation, by using heat sources.Stirling machines are also used to refrigerate environments, or inrefrigeration systems, mainly in systems with low capacity (below 100 W,in ASHRAE check point) and low storage temperatures (lower than −100°C.)

Such machines comprise a hermetic shell, within which is mounted amotor, which can be of the linear type driving a piston that compressesthe gas existing inside the shell. There are further provided, in theinterior of the hermetic shell, heat exchangers that are coupled to ahot external heat exchanger, or hot head, and to other heat exchangercoupled to a cold external heat exchanger, or cold head, both heatexchangers being produced in a metallic material with good thermalconductivity, which allows them to be capable to reject heat to theenvironment external to the machine and to absorb heat from anotherenvironment, respectively.

The Stirling machines generally have the heat of its hot head directedto a heat releasing environment, and its cold head is associated with arefrigeration system to refrigerate a determined environment.

The Stirling machine works by using, for example, helium as arefrigerant fluid, but other alternatives of refrigerant fluid may beused, such as hydrogen, or nitrogen, as described in Patent U.S. Pat.No. 5,927,079.

Stirling machines need auxiliary devices to allow transferring heat fromits hot heat exchanger to the environment whereto heat is desired to betransferred, as well as devices that allow heat to be absorbed from theenvironment requiring to be refrigerated through the cold head. Thereare known in the art some devices that allow effecting such heattransfers.

The known prior art presents different alternatives to make possiblesaid transfer, such as: employing auxiliary heat exchangers of thethermosiphon type, as taught in Patent U.S. Pat. No. 6,347,523;providing fins on the heads and using an auxiliary air movement system;using heat pipes; using a fluid pumping system employing pumps driven byone of the oscillating, mechanical, or electrical movements, amongothers.

In one of the known prior art solutions in which the Stirling machinesare used in a refrigeration system, as described in Patent U.S. Pat. No.5,927,079, the refrigeration of a determined environment is carried outby pumping a refrigerant fluid, under low temperature, which isrefrigerated by heat exchange while passing around the cold head of theStirling machine to an evaporator provided in the environment to berefrigerated. In this construction, the fluid under low temperature andrefrigerated in the cold head of the Stirling machine is conductedthrough the pipes of the evaporator by using pumping means disposedbetween the Stirling machine and the evaporator. In this construction,the removal of heat from the hot head of the Stirling machine isachieved by the circulation of water in a closed loop that passesthrough said hot head of the Stirling machine, which circulation is alsoachieved by action of a pump element mounted in the heat removing loop.

However, these known solutions present some disadvantages, such as inthe systems employing the thermosiphon as the working principle, theneed to level the component parts, such as pipes and heat exchangers.

In the case of the known solutions that use fins on the heads and heatexchange by air, the disadvantage resides in the fact that high heattransfer capacities are not possible to be achieved. In said systems, asaturation limit in relation to the heat transfer capacity is easilyreached. This is due to the efficiency saturation of the fins with theincrease of their length and/or decrease of the distance therebetween,or even due to the impossibility of finding air movement equipments withsufficient capacity to allow reaching the pressure and flowrate levelsrequired for determined heat transfer capacities. In addition, suchsolutions cause an increase in the level of vibrations of therefrigeration system and a reduction of reliability, as a function ofthe large quantity of the existing moving parts. The known solutionsthat use heat pipes further present the following disadvantage: highpressure loss of the system due to the necessary provision of a porousmaterial outside the evaporation region, which reduces the capacity totransfer heat at great distances.

OBJECTS OF THE INVENTION

Thus, it is an object of the present invention to provide arefrigeration system that uses a Stirling machine, which allowsachieving an efficient refrigeration of environments, without theproblems existing in the known solutions, such as low heat transfercapacity, pressure loss in the system, and low reliability.

Another object of the present invention is to provide a refrigerationsystem such as mentioned above, which reduces the need to levelcomponent parts of the system, such as pipes and heat exchangers.

A further object of the present invention is to provide a system such asproposed above, which presents minimum moving parts, reducing thepossibility of occurring vibration in the refrigeration system.

SUMMARY OF THE INVENTION

These and other objects are achieved through a refrigeration system ofthe type which comprises: a Stirling machine having a heating portionand a refrigerating portion; a refrigerating chamber; a first thermalenergy transfer device operatively associated with the refrigeratingportion and with the refrigerating chamber, so as to transfer the heatfrom the latter to the refrigerating portion by means of a circulatingfluid; a second thermal energy transfer device, operatively associatedwith a heat receiving means, external to said machine, and with theheating portion thereof, so as to transfer heat from the heating portionto the heat receiving means by means of a circulating fluid.

According to the invention, the first thermal energy transfer devicecomprises at least one capillary pump mounted in the refrigeratingchamber, in order to evaporate, by the heat absorbed from the latter andby action of the capillarity induced by said fluid passing through thecapillary pump, the circulating fluid received in said capillary pump; acondenser operatively coupled to the refrigerating portion of theStirling machine, in order to condense the circulating fluid received,in the gaseous state, from the capillary pump; and pipes to conduct in aclosed loop the circulating fluid, in the liquid state, from thecondenser to the capillary pump and, in the gaseous state, from thelatter to the condenser.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below, with reference to the encloseddrawings given by way of example for a preferred embodiment, and inwhich:

FIG. 1 is a schematic perspective view of the refrigeration system ofthe present invention, with the Stirling machine being operativelyassociated with an environment to be refrigerated;

FIG. 2 is a schematic perspective view of a construction for the thermalenergy transfer device of the refrigeration system of the presentinvention;

FIG. 3 is a longitudinal sectional view of a first construction for acapillary pump of the present invention driven by the heat removed fromthe environment to be refrigerated;

FIGS. 4, 5 and 6 are cross-sectional views of the first construction forthe capillary pump respectively taken according to lines IV-IV, V-V andVI-VI of FIG. 3;

FIG. 7 is a somewhat schematic partially cut perspective view of asecond construction for the capillary pump of the present inventiondriven by the heat removed from the heating portion of the Stirlingmachine;

FIG. 8 is a diametrical cross-sectional view of the second constructionfor the capillary pump illustrated in FIG. 7;

FIG. 9 is a cross-sectional view of the capillary pump of FIG. 7, takenaccording to line IX-IX of FIG. 8; and

FIG. 10 is a cross-sectional view of the capillary pump of FIG. 7, takenaccording to line X-X of FIG. 8.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

The refrigeration system of the present invention comprises a Stirlingmachine 1, for example of the type which uses a linear motor operativelyassociated with a first thermal energy transfer device 2 and a secondthermal energy transfer device 3, one of them being operatively coupledto a refrigerating chamber 4. In the example of the illustratedconstruction, the first thermal energy transfer device 2 is the oneassociated with the refrigerating chamber 4.

The Stirling machine 1 comprises, conventionally, a heating portion 1 aand a refrigerating portion 1 b, each one operatively connected to oneof the first and second thermal energy transfer devices 2, 3, asdescribed below.

According to the present invention, the first thermal energy transferdevice 2 contains a first circulating fluid to transfer thermal energybetween the refrigerating portion 1 b of the Stirling machine 1 and therefrigerating chamber 4, the second thermal energy transfer device 3containing a second circulating fluid to transfer thermal energy betweenthe heating portion 1 a of the Stirling machine 1 and a heat receivingmeans, which is usually the atmosphere or ambient air, maintaining acertain space from the machine.

In a way of carrying out the present invention, the first and the secondcirculating fluids are the same and defined for example, but notexclusively, by at least one of the elements selected from the groupconsisting of ether, water, and alcohol. It should be pointed out thatother types of circulating fluids are possible, without altering thescope of protection claimed herein.

According to the present invention, in one or in both the first and thesecond thermal energy transfer devices 2, 3, there is provided at leastone capillary pump, to be described below, through which passes arespective circulating fluid received in the liquid state and which,during its passage through said capillary pump, is submitted to a phasechange, passing from the liquid state to the gaseous state. Each one ofsaid first and second thermal energy transfer devices 2, 3, alsocomprises a respective heat exchanger, in which the respectivecirculating fluid coming from the capillary pump and in the gaseousstate is submitted to a phase change, passing to the liquid state.

According to the present invention, the first thermal energy transferdevice 2 comprises at least one capillary pump 10, associated with therefrigerating chamber 4 and presenting: a hermetic shell 11 providedwith an inlet 11 a for the circulating fluid in the liquid state, andwith an outlet 11 b for the circulating fluid in the gaseous state andwhich is disposed spaced from the inlet 11 a and separated from thelatter by a porous means 12, lodged inside the shell 11 and throughwhich the circulating fluid passes in its path from an inlet side to anoutlet side of the porous means, as it changes from the liquid state tothe gaseous state by the evaporation provoked by a heat source to whicha region of the shell 11 is exposed, and also by action of the pressureloss generated upon the fluid passing through the porous material,against which is seated the outlet side of the porous means 12 where theoutlet 11 b is provided.

In the first thermal energy transfer device 2, the heat source isrepresented by the air, which passes, preferably in a forced airflow,through the interior of the refrigerating chamber 4, in which is mountedthe capillary pump 10, or the assembly of capillary pumps 10, driven bythe heat removed from any environment to be refrigerated. In thisconstruction, the circulating fluid in the liquid state supplied to thecapillary pump 10 comes from a heat exchanger in the form of a condenser20 operatively coupled to the refrigerating portion 1 b of the Stirlingmachine 1 to transfer to said refrigerating portion 1 b the heat whichthe circulating fluid absorbed upon changing to the gaseous state in thecapillary pump 10, condensing said circulating fluid and allowing it toreturn, in the liquid state, back to the inlet 11 a of the shell 11 ofthe capillary pump 10.

As it can be noted in FIGS. 1 and 2, the capillary pump 10, or theassembly of capillary pumps 10, are connected to the condenser 20 by apair of pipes 30, 40, one of the latter being coupled to the inlet 11 afor the circulating fluid in the liquid state in each capillary pump 10,while the other pipe is coupled to the outlet 11 b for the circulatingfluid in the gaseous state of each capillary pump 10.

In the illustrated embodiment, the first thermal energy transfer device2 comprises a plurality of capillary pumps 10, disposed parallel inrelation to the respective closed loop of circulating fluid and whichare mounted inside the refrigerating chamber 4, so as to operate, inconjunction, as an evaporator to evaporate the circulating fluid, usingthe heat of the airflow F flowing through said refrigerating chamber 4.

In the construction illustrated in FIGS. 2-6, each capillary pump 10 hasits shell 11 defined by an elongated pipe, constructed in any adequatematerial and presenting high thermal conductivity, said shell 11 beingtransversally incorporated to a plurality of heat exchanging fins 13,which are parallel to and spaced from each other and arranged generallyparallel to the direction of the airflow F to be refrigerated and whichflows through said evaporator defined by the plurality of capillarypumps 10.

In said embodiment of FIGS. 2-6, the shell 11 in the form of anelongated pipe has an end defining the inlet 11 a and the opposite enddefining the outlet 11 b of the circulating fluid, said inlet 11 a andoutlet 11 b being separated from each other by a porous means 12,affixed to the inside of the shell 11 and also presenting a tubularshape, with an open end adjacent to the inlet 11 a to receive, in theinterior of the porous means 12, the circulating fluid in the liquidstate, and with a closed opposite end adjacent to the outlet 11 b of theshell 11. The porous means 12 has its external diameter dimensioned toallow it to be tightly seated in relation to the internal surface of theshell 11.

In order to allow the circulating fluid to radially traverse the annularthickness of the porous means 12 while evaporating to the gaseous state,and to allow said fluid to be captured to continue its path through theoutlet 11 b and through the pipe 40 toward the condenser 20,longitudinal passages 12 a are formed, between the porous means 12 andthe shell 11, having an end that is closed by the porous means 12 itselfnear the inlet 11 a, and an opposite end opened to the outlet 11 b.

In the illustrated embodiment, the longitudinal passages 12 a areobtained by the provision of respective longitudinal grooves in theexternal surface of the porous means 12. However, it should beunderstood that said grooves could be also provided along the internalsurface of the shell 11.

Considering that the condenser 20 of the first thermal energy transferdevice 2 transfers heat from the circulating fluid in the gaseous stateto the refrigerating portion 1 b of the Stirling machine 1, thiscondenser 20 preferably presents a cylindrical annular shell 21 with aninternal wall seated around the refrigerating portion 1 b, so as to beable to transfer heat, by conduction, to the latter.

The internal construction of the condenser 20 can be effected indifferent manners, provided that it allows achieving an efficientthermal exchange between the circulating fluid and the refrigeratingportion 1 b of the Stirling machine 1.

Anyway, the shell 21 of the condenser 20 is provided with an inlet 21 aand an outlet 21 b, which are respectively connected to the pipes 30, 40and the inlet 21 a and the outlet 21 b are interconnected inside theshell 21 by any connecting means, such as a coil immersed in a heatconducting means, for example a liquid in a simultaneous direct contactwith the internal wall of the shell 21 and with the connecting meansthat connects the inlet 21 a to the outlet 21 b.

As already mentioned in relation to the evaporator of the first thermalenergy transfer device 2, the condenser 20 should have its shell 21 andits internal component parts constructed in a material of high thermalconductivity and which resists both the working conditions of the systemand the circulating fluid that is used.

According to the description above, the first thermal energy transferdevice 2 is constructed to remove the heat from the refrigeratingchamber 4 by means of a circulating fluid that is impelled only by oneevaporator, operating jointly with a condenser and in the form of anassembly of parallel capillary pumps 10. The condenser is mounted to therefrigerating portion of the Stirling machine that works as an absorbingsource of the heat removed by the evaporator from the environment to berefrigerated.

However, the heat generated in the heating portion 1 a of the Stirlingmachine 1 must be transferred to an external means which is capable ofabsorbing said heat. This is the function of the second thermal energytransfer device 3, which also uses a circulating fluid to absorb theheat from the Stirling machine and to release said heat to theatmosphere or ambient air, as already mentioned above.

According to the construction illustrated in FIGS. 1, 7, 8, 9 and 10,the second thermal energy transfer device 3 comprises a capillary pump50 presenting an annular hermetic shell 51 provided with an externalinlet 51 a for the circulating fluid in the liquid state, and with aninternal outlet 51 b for the circulating fluid in the gaseous state andwhich is spaced from the inlet 51 a and separated from the latter by aporous means 52, which is also annular, lodged inside the shell 51, andthrough which the circulating fluid flows along its path and whilechanging from the liquid state to the gaseous state, by the evaporationcaused by a heat source placed in contact with the internal wall of thecylindrical annular shell 51, as well as by action of the pressure lossgenerated upon the fluid passing through the porous material.

In the construction mentioned above, the heat source is defined by theheating portion 1 a of the Stirling machine 1, around which it isaffixed, in direct contact, the internal wall of the shell 51 of thecapillary pump 50. The circulating fluid in the liquid state is suppliedto the capillary pump 50 from a condenser 60, which is positioned at acertain distance from the Stirling machine 1, so as to transfer to theatmosphere the heat which the circulating fluid absorbed upon changingto the gaseous state in the capillary pump 50, condensing said fluid andallowing it to return in the liquid state back to the inlet 51 a of theshell 51 of the capillary pump 50. The circulating fluid flows in pipes70, 80, which connect the inlet 51 a and the outlet 51 b of thecapillary pump 50 to an outlet 61 b and to an inlet 61 a of thecondenser 60, respectively. In the illustrated embodiment, the capillarypump 50 of the second thermal energy transfer device 3 presents an inlet51 a, which is disposed radially and medianly opened to an annular gap52 a defined between the porous means 52 and the external wall of theannular shell 51, in order to allow the circulating fluid in the liquidstate to be homogenously supplied around the porous means 52. Theopposite axial ends of the annular gap 52 a are closed by the seating ofthe porous means 52 against the external wall of the shell 51.

In the illustrated constructive example, the annular gap 52 a isobtained by the provision of an external circumferential recess in theporous means 52. It should however be understood that said recess couldbe also provided in the internal surface of the external wall of theshell 51.

With the construction described above, the circulating fluid in theliquid state penetrates in the annular gap 52 a through the inlet 51 aand starts its inward radial path, through the thickness of the porousmeans 52 and while evaporating to the gaseous state, said fluid beingthen captured to continue its path through the outlet 51 b and throughthe pipe 80 toward the condenser 60. For this purpose, longitudinalpassages 53 are formed between the porous means 52 and the internal wallof the shell 51. Said longitudinal passages, which can be defined bygrooves in the internal wall of the shell 51, are circumferentiallyinterconnected by a channel 54, generally positioned close to one of theends of the porous means 52 and whose interior communicates with theoutlet 51 b. In the illustrated embodiment, the channel 54 is defined byan internal circumferential recess provided in the porous means 52.

The internal wall of the shell 51 is shaped and dimensioned to seataround the heating portion 1 a of the Stirling machine 1, in order touse the heat produced thereby to evaporate the circulating fluidarriving at the longitudinal passages 53. The heat is transferred, byconduction, from the heating portion 1 a of the Stirling machine 1 tothe internal wall of the shell 51 of the capillary pump 50.

The condenser 60 to be used in the second thermal energy transfer device3 may present different constructions, provided they are adequate andcompatible with the operation of the capillary pump 50.

A possible construction for the condenser 60 is the one used for theevaporator of the first thermal energy transfer device 2. In this case,the condenser 60 comprises a plurality of tubular shells (notillustrated), which are parallel to each other and transversallyincorporated to a plurality of heat exchanging fins 63. The tubularshells have an end defining an inlet 61 a for the circulating fluid inthe gaseous state and which is connected to the pipe 80, and an oppositeend defining an outlet 61 b for the condensed circulating fluid, whichis already in the liquid state, after transferring the heat to theambient air, or to any other available heat absorbing means.

Within each tubular shell flows the circulating fluid, which transfersheat to the exterior, condenses and returns to the capillary pump 50.

The refrigeration system of the present invention can further comprise areservoir (not illustrated), associated with each thermal energytransfer device to control the working temperature by adjusting theamount of circulating fluid in each of the first and second thermalenergy transfer devices 2, 3 in relation to a given amount of heatsupplied to each of the capillary pumps 10, 50 of the present invention.Each circulating fluid transports heat from the hot region of therespective thermal energy transfer device to the cold region of the samethermal energy transfer device, as a function of the capillary forcesgenerated by the difference of surface tension in relation to thetemperature differential in each thermal energy transfer device.

The refrigeration system of the present invention can be furtherprovided, although not illustrated, with a system for the dynamicneutralization of vibrations, which minimizes the transmission of thevibrations, generated by the reciprocating movement of the piston of thelinear motor of the Stirling machine 1, to the shell and/or to othercomponents to which said machine is connected. These components aremounted within the hermetic shell, which supports the components andpromotes the tightness required in the compression and expansion strokesof the gas contained therein.

The refrigeration system of the present invention provides a pumpingsystem by capillary forces, which minimizes the difficulties of levelingthe system, pipes and heat exchangers in relation to each other. Therefrigeration system of the present invention also allows achieving ahigh heat transfer capacity, since it presents low pressure loss, thusallowing a higher heat transfer capacity to be achieved at greatdistances.

Besides the advantages above, the refrigeration system of the presentinvention allows achieving high levels of reliability, since it does notpresent moving parts and is protected from vibrations.

1. A refrigeration system comprising: a Stirling machine (1) having aheating portion (1 a) and a refrigerating portion (1 b); a refrigeratingchamber (4); a first thermal energy transfer device (2) operativelyassociated with the refrigerating portion (1 b) and with therefrigerating chamber (4), so as to transfer heat from the latter to therefrigerating portion (1 b) by means of a circulating fluid; a secondthermal energy transfer device (3), operatively associated with a heatreceiving means, external to said machine, and with the heating portion(1 a) thereof, so as to transfer heat from the heating portion (1 a) tothe heat receiving means by means of a circulating fluid, characterizedin that the first thermal energy transfer device (2) comprises at leastone capillary pump (10) mounted in the refrigerating chamber (4) inorder to evaporate, by the heat absorbed from the latter and by actionof the pressure loss generated by the fluid passing through thecapillary pump, the circulating fluid received in said capillary pump(10); a condenser (20) operatively coupled to the refrigerating portion(1 b) of the Stirling machine (1), in order to condense the circulatingfluid received, in the gaseous state, from the capillary pump (10); andpipes (30,40) to conduct, in a closed loop, the circulating fluid, inthe liquid state, from the condenser (20) to the capillary pump (10)and, in the gaseous state, from the latter to the condenser (20).
 2. Therefrigeration system according to claim 1, characterized in that thesecond thermal energy transfer device (3) comprises a capillary pump(50) operatively coupled to the heating portion (1) of the Stirlingmachine (1) in order to evaporate, by the heat absorbed from saidheating portion (1 a) and by action of the pressure loss generated bythe fluid passing through the capillary pump, the circulating fluidreceived in said capillary pump (50); a condenser (60) operativelyassociated with a heat receiving means external to the Stirling machine(1) in order to condense the circulating fluid received, in the gaseousstate, from the capillary pump (50); and pipes (70,80) to conduct in aclosed loop the circulating fluid, in the liquid state, from thecondenser (60) to the capillary pump (50) and, in the gaseous state,from the latter to the condenser (60).
 3. The refrigeration systemaccording to claim 1, characterized in that the capillary pump (10,50)comprises a shell (11,51), provided with an inlet (11 a, 51 a) for thecirculating fluid in the liquid state, and with an outlet (11 b, 51 b)for the circulating fluid in the gaseous state and which is spaced fromthe inlet (11 a, 51 a) and separated from the latter by a porous means(12,52) lodged inside the shell (11,51) and through which flows thecirculating fluid, by generation of said pressure loss, from an inletside to an outlet side of the porous means (12,52), due to the pressuredifference between both sides, while said circulating fluid is changingfrom the liquid state to the gaseous state, by evaporation, on theoutlet side of the porous means (12,52) that is exposed to the heatreceived from one of the parts defined by the refrigerating chamber (4)and the heating portion (1 a) of the Stirling machine (1).
 4. Therefrigeration system according to claim 3, characterized in that thecapillary pump (10) of the first thermal energy transfer device (2) hasa shell (11) in the form of an elongated pipe, which is transversallyincorporated to and traverses a plurality of heat exchanging fins (13),which are disposed parallel to the direction of an airflow (F) to berefrigerated and which passes through the capillary pump (10), one ofthe ends of the shell (11) defining the inlet (11 a) and the oppositeend defining the outlet (11 b) of the capillary pump (10), the porousmeans (12) presenting a tubular shape and having an end opened to theinlet (11 a) and an opposite closed end that is adjacent to the outlet(11 b), and longitudinal passages (12 a) being further provided, betweenthe porous means (12) and the shell (11), having closed ends that areadjacent to the inlet (11 a), and opposite ends opened to the outlet (11b) of the shell (11), said longitudinal passages directing thecirculating fluid, already in the gaseous state, to the outlet (11 b) ofthe shell (11).
 5. The refrigeration system according to claim 4,characterized in that the longitudinal passages (12 a) are defined bylongitudinal grooves provided in the porous means (12).
 6. Therefrigeration system according to claim 4, characterized in that aplurality of shells (11) are provided parallel to each other,incorporated to a plurality of fins (13), and mounted inside therefrigerating chamber (4).
 7. The refrigeration system according toclaim 3, characterized in that the capillary pump (50) of the secondthermal energy transfer device (3) presents a shell (51) of annularshape, with an external wall receiving the inlet (51 a) and with aninternal wall associated with the outlet (51 b), the porous means (52)having an annular shape and being lodged inside the shell (51), in orderto be seated against the internal and external walls of said shell (51),there being further provided: an annular gap (52 a) defined between theporous means (52) and the external wall of the shell (51) and into whichis opened the inlet (51 a); a plurality of longitudinal passages (53)between the porous means (52) and the internal wall of the shell (51);and a channel (54) interconnecting circumferentially the longitudinalpassages (53) and being opened to the outlet (51 b) of the shell (51).8. The refrigeration system according to claim 7, characterized in thatthe annular gap (52 a) is defined by an external circumferential recessprovided in the porous means (52).
 9. The refrigeration system accordingto claim 7, characterized in that the channel (54) is defined by aninternal circumferential recess provided close to one of the ends of theporous means (52).
 10. The refrigeration system according to claim 7,characterized in that the longitudinal passages (53) are defined bygrooves provided in the internal wall of the shell (51).
 11. Therefrigeration system according to claim 1, characterized in that thecondenser (20) of the first thermal energy transfer device (2) comprisesan annular shell (21), with an internal wall seated around therefrigerating portion (1 b) of the Stirling machine (1), so as totransfer heat, by conduction, to the latter, said shell (21) beingprovided with an inlet (21 a) and with an outlet (21 b), which arerespectively connected to pipes (40,30) that conduct the circulatingfluid in the gaseous state and in the liquid state, said inlet (21 a)and outlet (21 b) being interconnected inside the shell (21).
 12. Therefrigeration system according to claim 2, characterized in that thecondenser (60) of the second thermal energy transfer device (3)comprises a plurality of tubular shells which are parallel to each otherand transversally incorporated to a plurality of fins (63), said shellshaving an end defining an inlet (61 a) connected to the pipe (80) thatconducts the circulating fluid in the gaseous state, and an opposite enddefining an outlet (61 b) connected to the pipe (70) that conducts thecirculating fluid in the liquid state, said tubular shells and said fins(63) transferring heat to the environment in which the condenser (60) ismounted.
 13. The refrigeration system according to claim 2,characterized in that the capillary pump (10,50) comprises a shell(11,51), provided with an inlet (11 a, 51 a) for the circulating fluidin the liquid state, and with an outlet (11 b, 51 b) for the circulatingfluid in the gaseous state and which is spaced from the inlet (11 a, 51a) and separated from the latter by a porous means (12,52) lodged insidethe shell (11,51) and through which flows the circulating fluid, bygeneration of said pressure loss, from an inlet side to an outlet sideof the porous means (12,52), due to the pressure difference between bothsides, while said circulating fluid is changing from the liquid state tothe gaseous state, by evaporation, on the outlet side of the porousmeans (12,52) that is exposed to the heat received from one of the partsdefined by the refrigerating chamber (4) and the heating portion (1 a)of the Stirling machine (1).
 14. The refrigeration system according toclaim 13, characterized in that the capillary pump (10) of the firstthermal energy transfer device (2) has a shell (11) in the form of anelongated pipe, which is transversally incorporated to and traverses aplurality of heat exchanging fins (13), which are disposed parallel tothe direction of an airflow (F) to be refrigerated and which passesthrough the capillary pump (10), one of the ends of the shell (11)defining the inlet (11 a) and the opposite end defining the outlet (11b) of the capillary pump (10), the porous means (12) presenting atubular shape and having an end opened to the inlet (11 a) and anopposite closed end that is adjacent to the outlet (11 b), andlongitudinal passages (12 a) being further provided, between the porousmeans (12) and the shell (11), having closed ends that are adjacent tothe inlet (11 a), and opposite ends opened to the outlet (11 b) of theshell (11), said longitudinal passages directing the circulating fluid,already in the gaseous state, to the outlet (11 b) of the shell (11).15. The refrigeration system according to claim 13, characterized inthat the capillary pump (50) of the second thermal energy transferdevice (3) presents a shell (51) of annular shape, with an external wallreceiving the inlet (51 a) and with an internal wall associated with theoutlet (51 b), the porous means (52) having an annular shape and beinglodged inside the shell (51), in order to be seated against the internaland external walls of said shell (51), there being further provided: anannular gap (52 a) defined between the porous means (52) and theexternal wall of the shell (51) and into which is opened the inlet (51a); a plurality of longitudinal passages (53) between the porous means(52) and the internal wall of the shell (51); and a channel (54)interconnecting circumferentially the longitudinal passages (53) andbeing opened to the outlet (51 b) of the shell (51).
 16. Therefrigeration system according to claim 13, characterized in that theannular gap (52 a) is defined by an external circumferential recessprovided in the porous means (52).
 17. The refrigeration systemaccording to claim 13, characterized in that the channel (54) is definedby an internal circumferential recess provided close to one of the endsof the porous means (52).
 18. The refrigeration system according toclaim 13, characterized in that the longitudinal passages (53) aredefined by grooves provided in the internal wall of the shell (51).